Ultraviolet (uv) light-based refrigerant leak detection system and method

ABSTRACT

A leak detection system of a heating, ventilating, and air conditioning (HVAC) system includes a sensor configured to detect a UV tracer in a monitored gas volume of the HVAC system. The leak detection system also includes a controller communicatively coupled to the sensor. The controller is configured to modify operation of the HVAC system in response to the sensor detecting the UV tracer in the monitored gas volume.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Non-Provisional application claiming priority toU.S. Provisional Application No. 62/593,606, entitled “ULTRAVIOLET (UV)LIGHT-BASED REFRIGERANT LEAK DETECTION SYSTEM AND METHOD,” filed Dec. 1,2017, which is hereby incorporated by reference in its entirety for allpurposes.

BACKGROUND

The present disclosure relates generally to heating, ventilating, andair conditioning systems (HVAC) and, more particularly, to ultraviolet(UV)-based leak detection systems that are integrated into HVAC systems.

Residential, light commercial, commercial, and industrial HVAC systemsare used to control temperatures and air quality in residences andbuildings. Generally, the HVAC systems may circulate a refrigerantthrough a closed refrigeration circuit between an evaporator, where therefrigerant absorbs heat, and a condenser, where the refrigerantreleases heat. The refrigerant flowing within the refrigeration circuitis generally formulated to undergo phase changes within the normaloperating temperatures and pressures of the system so that quantities ofheat can be exchanged by virtue of the latent heat of vaporization ofthe refrigerant. As such, the refrigerant flowing within a HVAC systemtravels through multiple conduits and components of the refrigerationcircuit. Inasmuch as refrigerant leaks compromise system performance orresult in increased costs, for example, maintenance and/or operatingcosts, it is accordingly desirable to provide detection and responsesystems and methods for the HVAC system to reliably detect and respondto any refrigerant leaks of the HVAC system.

SUMMARY

In an embodiment, a leak detection system of a heating, ventilating, andair conditioning (HVAC) system includes a sensor configured to detect aUV tracer in a monitored gas volume of the HVAC system. The leakdetection system also includes a HVAC controller communicatively coupledto the sensor. The HVAC controller is configured to modify operation ofthe HVAC system in response to the sensor detecting the UV tracer in themonitored gas volume.

In another embodiment, a leak detection system of a heating,ventilating, and air conditioning (HVAC) system includes a vaporcompression system configured to circulate a refrigerant that includesan ultraviolet (UV) tracer. The leak detection system includes a sensorconfigured to measure a concentration of the UV tracer in a monitoredgas volume near the vapor compression system of the HVAC system. Theleak detection system also includes a controller configured to:determine a concentration of refrigerant in the monitored gas volumebased on the concentration of the UV tracer measured by the sensor; andmodify operation of the HVAC system when the concentration ofrefrigerant in the monitored gas volume is greater than a predeterminedthreshold value.

In another embodiment, the present disclosure relates to a method ofoperating a sensor to detect a refrigerant in a monitored gas volumeassociated with a heating, ventilation, and air conditioning (HVAC)system. A processor of a control unit of the HVAC system collects asample from a monitored gas volume. Next, the processor measures anamount of ultraviolet (UV) tracer in the sample. Next, the processordetermines an amount of refrigerant present in the monitored gas volumebased at least in part on the measured amount of UV tracer in thesample. Then, the processor modifies operation of the HVAC system inresponse to determining that the amount of leaked refrigerant in themonitored gas flow volume is greater than a predetermined thresholdvalue, wherein modifying comprises at least impeding the HVAC systemfrom activating.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a commercial or industrial HVAC system,in accordance with embodiments of the present technique;

FIG. 2 is an illustration of a packaged unit of the HVAC system shown inFIG. 1, in accordance with embodiments of the present technique;

FIG. 3 is an illustration of a split system of the HVAC system shown inFIG. 1, in accordance with embodiments of the present technique;

FIG. 4 is a schematic diagram of a refrigeration system of the HVACsystem shown in FIG. 1, in accordance with embodiments of the presenttechnique;

FIG. 5 is a schematic diagram of the HVAC system shown in FIG. 4including an integrated, UV-based leak detection system, in accordancewith embodiments of the present technique;

FIG. 6 is a schematic diagram of an UV tracer detection unit of theintegrated, UV-based leak detection system, in accordance embodiments ofthe present technique;

FIG. 7 is a schematic diagram of an UV tracer detection unit of theintegrated, UV-based leak detection system, in accordance embodiments ofthe present technique;

FIG. 8 is a schematic diagram of an UV tracer detection unit of theintegrated, UV-based leak detection system, in accordance embodiments ofthe present technique;

FIG. 9 is a schematic diagram of an UV tracer detection unit of theintegrated, UV-based leak detection system, in accordance embodiments ofthe present technique;

FIG. 10 is a schematic diagram of an UV tracer detection unit of theintegrated, UV-based leak detection system, in accordance embodiments ofthe present technique; and

FIG. 11 is a flow diagram representing a process for operating theintegrated, UV-based leak detection system of FIG. 5, in accordance withembodiments of the present technique.

DETAILED DESCRIPTION

As discussed above, a HVAC system generally includes a refrigerantflowing within a refrigeration circuit, also referred to herein as avapor compression system. The refrigerant flows through multipleconduits and components while undergoing phase changes to enable theHVAC system to condition an interior space of a building. For example,the refrigerant may be or include R32, R1234ze, R1234yf, R-454A, R-454C,R-455A, R-447A, R-452B, R-454B, or another suitable refrigerant.

In certain embodiments, the refrigerant may inadvertently leak from aflow path of the refrigeration circuit due to wear or degradation tocomponents, or imperfect joints or connections within the refrigerationcircuit. If undetected, a concentration of leaked refrigerant in theHVAC system may increase to or beyond a predefined concentrationthreshold. While certain refrigerant leaks may be difficult to directlydetect, it is presently recognized that UV tracers are generally moreeasily and/or accurately detected or measured than refrigerant gasesthemselves. As such, at least one UV tracer is included in theformulation of the refrigerant charge within the HVAC system tofacilitate the detection of refrigerant leaks by the disclosed leakdetection system. It may be noted that these UV tracers generally havesuitable physical properties and/or functionality to substantiallyminimize the effect of the UV tracer on the performance of therefrigerant within the refrigerant circuit of the HVAC system.

With the foregoing in mind, the present disclosure is directed to aUV-based leak detection system that is designed to be integrated into aHVAC system, and designed to indirectly detect leaked refrigerant in amonitored gas volume associated with the HVAC system. More specifically,the disclosed integrated, UV-based leak detection system (hereinafter“leak detection system”) detects a presence or concentration of leakedrefrigerant by optically measuring a concentration of UV tracers in asample of the monitored gas volume. Since these UV tracers are includedin the refrigerant formulation when the HVAC system is charged, they areable to escape from the refrigeration circuit along with leakingrefrigerant.

As discussed in detail below, the disclosed leak detection systemgenerally includes at least one UV sensor that uses UV light to measurea concentration of UV tracers in the sample of the monitored gas volume.To perform this UV-based measurement, the disclosed leak detectionsystem includes an UV light source that illuminates the sample of themonitored gas volume, and includes an UV light detector that measures anintensity of UV light that is modified by interacting with UV tracerspresent in the sample. Additionally, a HVAC controller, or anothersuitable controller or processor of the system, can determine thepresence or concentration of leaked refrigerant in the monitored gasvolume based on the measurements of the UV light detector.

Furthermore, since the disclosed leak detection system is integratedinto the HVAC system, the HVAC controller, or another suitablecontroller, can coordinate operation of the leak detection system, aswell as the remainder HVAC system. For example, as discussed below, toenhance leak detection, the HVAC controller may prompt the UV sensor toparticularly collect and analyze samples for UV tracers after switchingthe HVAC system to an idle state or off-cycle. Additionally, the HVACcontroller can modify operation of the HVAC system in response todetermining that the concentration of leaked refrigerant exceeds apredetermined threshold value. For example, the HVAC controller canprovide suitable control signals to halt operation or to preventreactivation of the HVAC system, as well as provide an audible or visualalarm indicating the detected refrigerant leak. As such, the presentlydisclosed leak detection system enables the HVAC system to reliablydetect and respond to refrigerant leaks.

Turning now to the drawings, FIG. 1 illustrates a heating, ventilating,and air conditioning (HVAC) system for building environmental managementthat may employ one or more HVAC units. In the illustrated embodiment, abuilding 10 is air conditioned by a system that includes a HVAC unit 12.The building 10 may be a commercial structure or a residentialstructure. As shown, the HVAC unit 12 is disposed on the roof of thebuilding 10; however, the HVAC unit 12 may be located in other equipmentrooms or areas adjacent the building 10. The HVAC unit 12 may be asingle package unit containing other equipment, such as a blower,integrated air handler, and/or auxiliary heating unit. In otherembodiments, the HVAC unit 12 may be part of a split HVAC system, suchas the system shown in FIG. 3, which includes an outdoor HVAC unit 58and an indoor HVAC unit 56.

The HVAC unit 12 is an air cooled device that implements a refrigerationcycle to provide conditioned air to the building 10. Specifically, theHVAC unit 12 may include one or more heat exchangers across which an airflow is passed to condition the air flow before the air flow is suppliedto the building. In the illustrated embodiment, the HVAC unit 12 is arooftop unit (RTU) that conditions a supply air stream, such asenvironmental air and/or a return air flow from the building 10. Afterthe HVAC unit 12 conditions the air, the air is supplied to the building10 via ductwork 14 extending throughout the building 10 from the HVACunit 12. For example, the ductwork 14 may extend to various individualfloors or other sections of the building 10. In certain embodiments, theHVAC unit 12 may be a heat pump that provides both heating and coolingto the building with one refrigeration circuit configured to operate indifferent modes. In other embodiments, the HVAC unit 12 may include oneor more refrigeration circuits for cooling an air stream and a furnacefor heating the air stream.

A control device 16, one type of which may be a thermostat, may be usedto designate the temperature of the conditioned air. The control device16 also may be used to control the flow of air through the ductwork 14.For example, the control device 16 may be used to regulate operation ofone or more components of the HVAC unit 12 or other components, such asdampers and fans, within the building 10 that may control flow of airthrough and/or from the ductwork 14. In some embodiments, other devicesmay be included in the system, such as pressure and/or temperaturetransducers or switches that sense the temperatures and pressures of thesupply air, return air, and so forth. Moreover, the control device 16may include computer systems that are integrated with or separate fromother building control or monitoring systems, and even systems that areremote from the building 10.

FIG. 2 is a perspective view of an embodiment of the HVAC unit 12. Inthe illustrated embodiment, the HVAC unit 12 is a single package unitthat may include one or more independent refrigeration circuits andcomponents that are tested, charged, wired, piped, and ready forinstallation. The HVAC unit 12 may provide a variety of heating and/orcooling functions, such as cooling only, heating only, cooling withelectric heat, cooling with dehumidification, cooling with gas heat, orcooling with a heat pump. As described above, the HVAC unit 12 maydirectly cool and/or heat an air stream provided to the building 10 tocondition a space in the building 10.

As shown in the illustrated embodiment of FIG. 2, a cabinet 24 enclosesthe HVAC unit 12 and provides structural support and protection to theinternal components from environmental and other contaminants. In someembodiments, the cabinet 24 may be constructed of galvanized steel andinsulated with aluminum foil faced insulation. Rails 26 may be joined tothe bottom perimeter of the cabinet 24 and provide a foundation for theHVAC unit 12. In certain embodiments, the rails 26 may provide accessfor a forklift and/or overhead rigging to facilitate installation and/orremoval of the HVAC unit 12. In some embodiments, the rails 26 may fitinto “curbs” on the roof to enable the HVAC unit 12 to provide air tothe ductwork 14 from the bottom of the HVAC unit 12 while blockingelements such as rain from leaking into the building 10.

The HVAC unit 12 includes heat exchangers 28 and 30 in fluidcommunication with one or more refrigeration circuits. Tubes within theheat exchangers 28 and 30 may circulate refrigerant through the heatexchangers 28 and 30. For example, the refrigerant may be R-410A. Thetubes may be of various types, such as multichannel tubes, conventionalcopper or aluminum tubing, and so forth. Together, the heat exchangers28 and 30 may implement a thermal cycle in which the refrigerantundergoes phase changes and/or temperature changes as it flows throughthe heat exchangers 28 and 30 to produce heated and/or cooled air. Forexample, the heat exchanger 28 may function as a condenser where heat isreleased from the refrigerant to ambient air, and the heat exchanger 30may function as an evaporator where the refrigerant absorbs heat to coolan air stream. In other embodiments, the HVAC unit 12 may operate in aheat pump mode where the roles of the heat exchangers 28 and 30 may bereversed. That is, the heat exchanger 28 may function as an evaporatorand the heat exchanger 30 may function as a condenser. In furtherembodiments, the HVAC unit 12 may include a furnace for heating the airstream that is supplied to the building 10. While the illustratedembodiment of FIG. 2 shows the HVAC unit 12 having two of the heatexchangers 28 and 30, in other embodiments, the HVAC unit 12 may includeone heat exchanger or more than two heat exchangers.

The heat exchanger 30 is located within a compartment 31 that separatesthe heat exchanger 30 from the heat exchanger 28. Fans 32 draw air fromthe environment through the heat exchanger 28. Air may be heated and/orcooled as the air flows through the heat exchanger 28 before beingreleased back to the environment surrounding the rooftop unit 12. Ablower assembly 34, powered by a motor 36, draws air through the heatexchanger 30 to heat or cool the air. The heated or cooled air may bedirected to the building 10 by the ductwork 14, which may be connectedto the HVAC unit 12. Before flowing through the heat exchanger 30, theconditioned air flows through one or more filters 38 that may removeparticulates and contaminants from the air. In certain embodiments, thefilters 38 may be disposed on the air intake side of the heat exchanger30 to prevent contaminants from contacting the heat exchanger 30.

The HVAC unit 12 also may include other equipment for implementing thethermal cycle. Compressors 42 increase the pressure and temperature ofthe refrigerant before the refrigerant enters the heat exchanger 28. Thecompressors 42 may be any suitable type of compressors, such as scrollcompressors, rotary compressors, screw compressors, or reciprocatingcompressors. In some embodiments, the compressors 42 may include a pairof hermetic direct drive compressors arranged in a dual stageconfiguration 44. However, in other embodiments, any number of thecompressors 42 may be provided to achieve various stages of heatingand/or cooling. As may be appreciated, additional equipment and devicesmay be included in the HVAC unit 12, such as a solid-core filter drier,a drain pan, a disconnect switch, an economizer, pressure switches,phase monitors, and humidity sensors, among other things.

The HVAC unit 12 may receive power through a terminal block 46. Forexample, a high voltage power source may be connected to the terminalblock 46 to power the equipment. The operation of the HVAC unit 12 maybe governed or regulated by a control board 48. The control board 48 mayinclude control circuitry connected to a thermostat, sensors, andalarms. One or more of these components may be referred to hereinseparately or collectively as the control device 16. The controlcircuitry may be configured to control operation of the equipment,provide alarms, and monitor safety switches. Wiring 49 may connect thecontrol board 48 and the terminal block 46 to the equipment of the HVACunit 12.

FIG. 3 illustrates a residential heating and cooling system 50, also inaccordance with present techniques. The residential heating and coolingsystem 50 may provide heated and cooled air to a residential structure,as well as provide outside air for ventilation and provide improvedindoor air quality (IAQ) through devices such as ultraviolet lights andair filters. In the illustrated embodiment, the residential heating andcooling system 50 is a split HVAC system. In general, a residence 52conditioned by a split HVAC system may include refrigerant conduits 54that operatively couple the indoor unit 56 to the outdoor unit 58. Theindoor unit 56 may be positioned in a utility room, an attic, abasement, and so forth. The outdoor unit 58 is typically situatedadjacent to a side of residence 52 and is covered by a shroud to protectthe system components and to prevent leaves and other debris orcontaminants from entering the unit. The refrigerant conduits 54transfer refrigerant between the indoor unit 56 and the outdoor unit 58,typically transferring primarily liquid refrigerant in one direction andprimarily vaporized refrigerant in an opposite direction.

When the system shown in FIG. 3 is operating as an air conditioner, aheat exchanger 60 in the outdoor unit 58 serves as a condenser forre-condensing vaporized refrigerant flowing from the indoor unit 56 tothe outdoor unit 58 via one of the refrigerant conduits 54. In theseapplications, a heat exchanger 62 of the indoor unit functions as anevaporator. Specifically, the heat exchanger 62 receives liquidrefrigerant (which may be expanded by an expansion device) andevaporates the refrigerant before returning it to the outdoor unit 58.

The outdoor unit 58 draws environmental air through the heat exchanger60 using a fan 64 and expels the air above the outdoor unit 58. Whenoperating as an air conditioner, the air is heated by the heat exchanger60 within the outdoor unit 58 and exits the unit at a temperature higherthan it entered. The indoor unit 56 includes a blower or fan 66 thatdirects air through or across the indoor heat exchanger 62, where theair is cooled when the system is operating in air conditioning mode.Thereafter, the air is passed through ductwork 68 that directs the airto the residence 52. The overall system operates to maintain a desiredtemperature as set by a system controller. When the temperature sensedinside the residence 52 is higher than the set point on the thermostat,or the set point plus a small amount, the residential heating andcooling system 50 may become operative to refrigerate additional air forcirculation through the residence 52. When the temperature reaches theset point, or the set point minus a small amount, the residentialheating and cooling system 50 may stop the refrigeration cycletemporarily.

The residential heating and cooling system 50 may also operate as a heatpump. When operating as a heat pump, the roles of heat exchangers 60 and62 are reversed. That is, the heat exchanger 60 of the outdoor unit 58will serve as an evaporator to evaporate refrigerant and thereby coolair entering the outdoor unit 58 as the air passes over outdoor the heatexchanger 60. The indoor heat exchanger 62 will receive a stream of airblown over it and will heat the air by condensing the refrigerant.

In some embodiments, the indoor unit 56 may include a furnace system 70.For example, the indoor unit 56 may include the furnace system 70 whenthe residential heating and cooling system 50 is not configured tooperate as a heat pump. The furnace system 70 may include a burnerassembly and heat exchanger, among other components, inside the indoorunit 56. Fuel is provided to the burner assembly of the furnace 70 whereit is mixed with air and combusted to form ultraviolet tracers. Theultraviolet tracers may pass through tubes or piping in a heat exchangerthat is separate from heat exchanger 62, such that air directed by theblower 66 passes over the tubes or pipes and extracts heat from theultraviolet tracers. The heated air may then be routed from the furnacesystem 70 to the ductwork 68 for heating the residence 52.

FIG. 4 is an embodiment of a vapor compression system 72 that can beused in any of the systems described above. The vapor compression system72 may circulate a refrigerant through a circuit starting with acompressor 74. The circuit may also include a condenser 76, an expansionvalve(s) or device(s) 78, and an evaporator 80. The vapor compressionsystem 72 may further include a control panel 82 that has an analog todigital (A/D) converter 84, a microprocessor 86, a non-volatile memory88, and/or an interface board 90. The control panel 82 and itscomponents may function to regulate operation of the vapor compressionsystem 72 based on feedback from an operator, from sensors of the vaporcompression system 72 that detect operating conditions, and so forth.

In some embodiments, the vapor compression system 72 may use one or moreof a variable speed drive (VSDs) 92, a motor 94, the compressor 74, thecondenser 76, the expansion valve or device 78, and/or the evaporator80. The motor 94 may drive the compressor 74 and may be powered by thevariable speed drive (VSD) 92. The VSD 92 receives alternating current(AC) power having a particular fixed line voltage and fixed linefrequency from an AC power source, and provides power having a variablevoltage and frequency to the motor 94. In other embodiments, the motor94 may be powered directly from an AC or direct current (DC) powersource. The motor 94 may include any type of electric motor that can bepowered by a VSD or directly from an AC or DC power source, such as aswitched reluctance motor, an induction motor, an electronicallycommutated permanent magnet motor, or another suitable motor.

The compressor 74 compresses a refrigerant vapor and delivers the vaporto the condenser 76 through a discharge passage. In some embodiments,the compressor 74 may be a centrifugal compressor. The refrigerant vapordelivered by the compressor 74 to the condenser 76 may transfer heat toa fluid passing across the condenser 76, such as ambient orenvironmental air 96. The refrigerant vapor may condense to arefrigerant liquid in the condenser 76 as a result of thermal heattransfer with the environmental air 96. The liquid refrigerant from thecondenser 76 may flow through the expansion device 78 to the evaporator80.

The liquid refrigerant delivered to the evaporator 80 may absorb heatfrom another air stream, such as a supply air stream 98 provided to thebuilding 10 or the residence 52. For example, the supply air stream 98may include ambient or environmental air, return air from a building, ora combination of the two. The liquid refrigerant in the evaporator 80may undergo a phase change from the liquid refrigerant to a refrigerantvapor. In this manner, the evaporator 80 may reduce the temperature ofthe supply air stream 98 via thermal heat transfer with the refrigerant.Thereafter, the vapor refrigerant exits the evaporator 80 and returns tothe compressor 74 by a suction line to complete the cycle.

In some embodiments, the vapor compression system 72 may further includea reheat coil in addition to the evaporator 80. For example, the reheatcoil may be positioned downstream of the evaporator relative to thesupply air stream 98 and may reheat the supply air stream 98 when thesupply air stream 98 is overcooled to remove humidity from the supplyair stream 98 before the supply air stream 98 is directed to thebuilding 10 or the residence 52.

It should be appreciated that any of the features described herein maybe incorporated with the HVAC unit 12, the residential heating andcooling system 50, or other HVAC systems. Additionally, while thefeatures disclosed herein are described in the context of embodimentsthat directly heat and cool a supply air stream provided to a buildingor other load, embodiments of the present disclosure may be applicableto other HVAC systems as well. For example, the features describedherein may be applied to mechanical cooling systems, free coolingsystems, chiller systems, or other heat pump or refrigerationapplications.

FIG. 5 is a diagram illustrating an embodiment of a leak detectionsystem 101 having an ultraviolet (UV) tracer sensor 100 that iscommunicatively coupled to the control panel 82 of the HVAC unit 12. Incertain embodiments, the UV tracer sensor 100 may be integrated into theHVAC unit 12 during manufacturing, retrofitted into existing HVAC units12 after manufacturing, or implemented as an external sensor that iscommunicatively coupled to the control panel 82 via a wired or wirelesscommunication channel. For example, the UV tracer sensor 100 may bedisposed in the ductwork 14. As such, the UV tracer sensor 100 iscapable of providing signals to the control panel 82 that are indicativeof the presence or absence of refrigerant within a sample 104 of air.

The disclosed UV tracer sensor 100 generally collects the sample 104 ofgas from a monitored gas volume 106 to determine whether a leakedrefrigerant is present within the sample 104. As illustrated in FIG. 5,the UV tracer sensor 100 is fluidly coupled to a monitored gas volume106 near the evaporator 80 of the HVAC unit 12 via a valve 108. As such,the UV tracer sensor 100 is capable of receiving the sample 104 from themonitored gas volume 106. In certain embodiments, the leak detectionsystem 101 may include one or more UV tracer sensors 100 disposed withinthe cabinet 24 of the HVAC unit 12, or within the casing 110 of theoutdoor HVAC unit 58, or within the casing 111 of the indoor HVAC unit56, and the monitored gas volume 106 corresponds to an interior airvolume within the casing or packaging of these respective units, asindicated FIGS. 2 and 3. As discussed above in certain embodiments, theUV tracer sensor 100 may be disposed near the indoor heat exchanger 62,or evaporator 62. For example, the UV tracer sensor 100 may be disposedwithin a few inches, adjacent to, or directly below the evaporator 62.In other embodiments, a UV tracer sensor 100 may be disposed within theductwork 14 of the building 10, as illustrated in FIGS. 1 and 4, and themonitored gas volume 106 corresponds to an interior air volume withinthe ductwork 14.

The illustrated embodiment of the UV tracer sensor 100 includes acontrol unit 102, a sample preparation unit 112, and an UV tracerdetection unit 114 that cooperate to enable the UV tracer sensor 100 tofunction as disclosed. In general, the sample preparation unit 112collects the sample 104 from the monitored gas volume 106 and preparesthe sample for detection, the UV tracer detection unit 114 identifies UVtracers in the prepared sample, and the control unit 102 controls theoperation of the other units. In other embodiments, the UV tracer sensor100 may lack the control unit 102 and the microprocessor 86 of thecontrol panel 82 may control operation of other units of the UV tracersensor 100, as set forth herein. Additionally, certain embodiments ofthe UV tracer sensor 100 may lack the sample preparation unit 112, andthe UV tracer detection unit 114 may detect UV tracers in the sample 104without extracting, collecting, or otherwise removing the sample fromthe monitored gas volume 106.

The control unit 102 of the illustrated embodiment of the UV tracersensor 100 includes a processor 116 and memory 118. The memory 118stores computer readable instructions that are executed by the processor116 to control operation of the UV tracer sensor 100. For example, basedon these instructions, the processor 116 can provide suitable controlsignals to activate, deactivate, and/or modify operation of the variouscomponents of the UV tracer sensor 100 to enable the sensor to detectand/or measure an amount of leaked refrigerant in the sample 104.Additionally, the processor 116 can determine a presence orconcentration of leaked refrigerant in the sample 104 based on thesignals received from the UV tracer detection unit 114, as discussedbelow.

For the embodiment illustrated in FIG. 5, the sample preparation unit112 of the UV tracer sensor 100 includes suitable elements to preparethe sample 104 for detection by the UV tracer detection unit 114. Forexample, the illustrated sample preparation unit 112 includes a valve108 that is communicatively coupled to the processor 116 of the controlunit 102. As such, the control unit 102 can provide suitable controlsignals to monitor and adjust the position of the valve 108 to controlan amount or rate that the sample 104 is collected from the monitoredgas volume 106. In other embodiments, the sample preparation unit 112may include dampers, adjustable louvers, or other suitable flow controlmechanism, in accordance with the present disclosure. In certainembodiments, the sample preparation unit 112 may include an air movingdevice. For example, the air moving device may be a fan, blower, orcompressor. In certain embodiments, the sample preparation unit 112 mayinclude one or more filters to remove particulates, moisture, or othercomponents from the sample 104 that might interfere with later analysisfor UV tracers. In certain embodiments, the sample preparation unit 112may include a heater or another suitable mechanism device to warm thesample 104. Additionally, it is presently recognized that compressingthe sample might increase the concentration of UV tracers (per unitvolume) in the sample, and as such, in certain embodiments, the samplepreparation unit 112 may include a compressor that compresses the samplefor UV analysis.

In the illustrated embodiment, the UV tracer detection unit 114 isfluidly coupled to the sample preparation unit 112 and receives thesample gas flow 122 from the sample preparation unit 112. The UV tracerdetection unit 114 includes at least one UV light source 124 illuminatesthe sample gas flow 122 and at least one light detector 126 thatinteracts with and measures the intensity of light from the UV lightsource 124. The intensity of light that may change based on the presenceor absence of UV tracers in the sample gas flow 122. Additionally, theintensity of the light may be proportional to the concentration of UVtracers present in the gas flow. The UV light source 124 may be alight-emitting diode (LED), laser, or lamp. As such, the light detector126 is communicatively coupled to the processor 116 of the control unit102 to provide suitable signals that are indicative of the presence orconcentration of UV tracers present in the sample gas flow 122. Incertain embodiments, the light detector 126 may directly measure achange in an optical property, such as a change in absorption,scattering, emission, fluorescence, and luminescence, as a result of thesample gas flow 122 that is indicative of the presence or concentrationof a UV tracer. Additionally, the light detector 126 is fluidly coupledto the external environment and releases the sample gas flow 122 fromthe UV tracer sensor 100 after traversing the UV tracer detection unit114.

Based on signals received from the light detector 126 of the UV tracerdetection unit 114, the processor 116 of the control unit 102 may send asignal to the microprocessor 86 of the control panel 82 to modifyoperation of the HVAC unit 12. Modifying the HVAC unit 12 may includeshutting down the HVAC unit 12, preventing reactivation of the HVAC unit12, sending a signal to a user, such as an audible or visual signal. Itis also presently recognized that it can be advantageous to control theoperation of the UV tracer sensor 100 based on the state of the HVACunit 12, in certain embodiments. For example, the HVAC can detectrefrigerant gases prior to reactivation of the HVAC system to mitigateany potential risks of ignition. In certain embodiments, the controlpanel 82 may send signals to the control unit 102 to control operationof the UV tracer sensor 100. For example, the microprocessor 86 of thecontrol panel 82 might send signals to the processor 116 of the controlunit 102 indicating whether the HVAC system is in an idle state. Forexample, an idle state may be that the compressor 74 of the vaporcompression system 72 is deactivated, or that fans associated with thecondenser 76 and/or evaporator 80 are deactivated. As such, in certainembodiments, the control panel 82 and control unit 102 may cooperate toactivate the UV tracer sensor 100 based on the state of the HVAC system.As mentioned, during operation of the UV tracer sensor 100, the UVtracer detection unit 114 provides signals indicative of the presence ofleaked refrigerant gas in the sample 104. Based on the data received bythe control unit 102 from the UV tracer detection unit 114, the controlunit 102 makes a determination whether to send a signal to the controlpanel 82 and/or an alert or alarm indication to a user.

Returning briefly to FIG. 3, the outdoor HVAC unit 58 and indoor HVACunit 56 are illustrated as including one or more UV tracer sensors 100disposed in one or more positions within the HVAC system. It may benoted that, in certain embodiments, the blower 66 may not always bedisposed at the bottom of the indoor HVAC unit 56. As shown, the UVtracer sensor 100 is disposed in an outdoor HVAC unit 58. Suitablelocations for the UV tracer sensor 100 include locations that havelimited ambient light exposure to prevent interference with UV tracerdetection unit 114. As also shown, the UV tracer sensor 100 may bedisposed in the indoor HVAC unit 56. For example, as illustrated, the UVtracer sensor 100 may be disposed near a heat exchanger 62, or withinthe ductwork 14. It is presently recognized that disposing the UV tracersensor 100 in the ductwork 14, near the heat exchanger 60, and/or nearthe heat exchanger 62 may enable the UV tracer sensor 100 to acquire agreater concentration of UV tracer during a leak, as the UV tracersensor 100 is closer to the vapor compression system 72 and, therefore,the potential refrigerant leak. For example, the UV tracer sensor 100may be disposed near the vapor compression system 62, the heat exchanger60, and/or heat exchanger 62. In this context, “near” may be within afew inches, adjacent to, or directly below the heat exchangers 60 and/or62. As stated above, the UV tracer sensor 100 may be disposed near theheat exchangers, particularly the evaporator 62 of an indoor HVAC unit,to analyze samples 104 having leaked refrigerant that collects below theevaporator 62, particularly when the HVAC unit 56 is idle.

FIG. 6 is a schematic diagram illustrating an embodiment of the UVtracer detection unit 114 of the UV tracer sensor 100, in accordancewith the present technique. More specifically, the light detector 126illustrated in FIG. 6 optically detects or measures the presence orconcentration of UV tracers in the sample gas flow 122. The illustratedembodiment includes an UV light source 124 and a light detector 126. TheUV light source 124 generates emitted light 130 having an intensity thatis detected by the light detector 126. During operation of theembodiment of the UV tracer detection unit 114 illustrated in FIG. 6,emitted light 130 from the UV light source 124 that interacts with thesample gas flow 122 received from the sample preparation units 112 mayresult in modified light 138. Modified light 138 may result from emittedlight 130 that is scattered, absorbed, or absorbed and subsequentlyreemitted, for example, through fluorescence or Raman. The modifiedlight 138 may have an intensity that differs from the intensity of theemitted light, which is proportional to the concentration of UV tracerin the sample gas flow 122, and/or frequency of light emitted by the UVlight source 124. In certain embodiments, no modified light 138 isdetected by the light detector 128, indicating that the amount of UVtracer present in the sample gas flow 122 was sufficient enough to blockthe emitted light 130 from reaching the light detector 128. The lightdetector 128 is disposed in suitable positions downstream from the UVlight source 124 to detect a change in the emitted light 130 based onthe presence of UV tracers in the sample gas flow 122. The illustratedembodiment also includes an outlet 113 which allows the gas to flow outof the UV tracer detection unit 114 after measuring the presence orconcentration of UV tracers in the sample gas flow 122.

FIG. 7 is a schematic diagram of another embodiment of the UV tracerdetection unit 114 of the UV tracer sensor 100, in accordance with thepresent technique. The UV tracer detection unit 114 may detect apresence or concentration of UV tracers using the light detector 128based on a change in the initial intensity and/or frequency of lightfrom the UV light source 124. The UV tracer detection unit 114illustrated in FIG. 7 includes multiple mirrors 128 a, 128 b, 128 c, 128d, 128 e, 128 f that increase the path length of emitted light 130 fromthe UV light source 124 before detection. As such, the emitted light 130interacts with a greater volume of sample gas flow 122. When UV tracersare present in the sample gas flow 122 as the result of a refrigerantleak, this results in a more pronounced change in the intensity and/orfrequency of the emitted light 130 that is subsequently measured by thelight detector 128. Additionally, the intensity of the light may beproportional to the amount or concentration of UV tracer present in thesample gas flow 122. The illustrated embodiment also includes an outlet113 which allows the gas to flow out of the UV tracer detection 114after measuring the presence or concentration of UV tracers in thesample gas flow 122.

FIG. 8 is a schematic diagram of another embodiment of the UV tracerdetection unit 114 of the UV tracer sensor 100, in accordance with thepresent technique. More specifically, the UV tracer detection unit 114may be used in embodiments of the UV tracer sensor 100 that do notinclude a sample preparation unit 112, and that instead measure thesample 104 within the monitored gas volume 106. The UV tracer detectionunit 114 illustrated in FIG. 8 contains a light source 124 and a lightdetector 126 that is positioned downstream of a path of the emittedlight 130. In operation, the light detector 126 detects a change in theintensity of light emitted by the UV light source 124 that results fromthe emitted light 130 interacting with the sample gas flow 122.Additionally, the UV tracer sensor 100 illustrated in FIG. 8 includes areflective coating material 134 lining the inner wall of ductwork 68.For example, the reflective coating material 134 may be paint ormirrors. As illustrated, the light from the light source may bereflected multiple times through a sample 104 of a monitored gas volume106 before reaching the detector, thus enabling the UV tracer sensor 100to sample a substantial volume of air traversing the ductwork 68. In oneembodiments, the reflective coating material 134 may be disposed on aninner surface of the cabinet 24 of the HVAC unit 12. In anotherembodiment, the reflective coating material 134 may be disposed on aninner surface of a casing 110 of the indoor HVAC unit 56, and/or on aninner surface of the casing 110 of the outdoor HVAC unit 58 to enabledetection of UV tracers from leaked refrigerant that accumulates withinan interior volume of these packages.

FIG. 9 is a schematic diagram of another embodiment the UV tracerdetection unit 114 of the UV tracer sensor 100 that includes a camera136. In operation, a UV light source 124 generates emitted light 130that is directed to a sample gas flow 122. A modified light 138 isgenerated based on the interaction between the emitted light 130 and thesample gas flow 122. For example, if a UV tracer is present in thesample gas flow 122, the UV tracer may scatter, or absorb and luminesceto generate modified light 138. The modified light 138 may havedifferent optical properties than the emitted light, which can bemeasured by the camera 136. Different optical properties may include achange in color, frequency, or intensity of light. For example, if no UVtracers are present in the sample gas flow 122, the camera 136 maydetect little to no light. When UV tracers are present, the resultingmodified light 138 be a different color, frequency, or intensity basedon the interaction between the emitted light 130 and the sample gas flow122.

A magnitude of the change in color, frequency, and intensity may be usedto determine an amount of UV tracers present in the sample gas flow 122.Then, the UV tracer detection unit 114 may send data signals to themicroprocessor 86 of the control panel 82, or processor 116 of thecontrol unit 102, which contain the pixel values of the images recordedby the camera 136. Based on the data signals, the microprocessor 86 mayperform calculations to determine the presence of UV tracers in thesample gas flow 122. For example, a difference in the colors of eachpixel may indicate optical processes, such as scattering orphotoluminescence by the UV tracers, have occurred. The microprocessor86 may compare pixel values of the image to a predefined threshold that,above or below the threshold, indicates the presence or absence of UVtracers in the sample gas. Additionally, the microprocessor 86 maydetermine a concentration of UV tracer present in the sample gas flow122 based on the pixel values or integrated pixel values of the imagetaken by the camera 136. In certain embodiments, the microprocessor 86may compare the image a background image. The illustrated embodimentalso includes an outlet 113 which allows the gas to flow out of the UVtracer detection unit 114 after measuring the presence or concentrationof UV tracers in the sample gas flow 122.

FIG. 10 is a schematic diagram of an embodiment of the UV tracerdetection unit 114 of the UV tracer sensor 100, in accordance with thepresent technique. The embodiment of the UV tracer detection unit 114illustrated in FIG. 10 includes a circuit 140 that is disposeddownstream from the UV light source 124. Additionally, the circuit 140of the illustrated embodiment includes a photovoltaic material 142disposed in a suitable position to receive the emitted light 130 fromthe UV light source 124. The photovoltaic material 142 may be a metaloxide, semiconductor, or organic solar. During operation of theembodiment of the UV tracer sensor 100 illustrated in FIG. 10, thephotovoltaic material 142 generates an electrical signal as a result ofthe emitted light 130 incident on the photovoltaic material. The samplegas flow 122 received from the sample preparation unit 112 mayconstitute UV tracers that interact with the emitted light 130. UVtracers present in the sample gas flow 122 would reduce or block theamount of the emitted light 130 reaching the photovoltaic device,resulting in a change of a measurement electrical signal. In certainembodiments, the circuit 140 includes a multi-meter 144 communicativelycoupled to the processor 116 of the control unit 102. The multi-meter144 provides suitable signals to indicate changes in the amount of lightreceived by the photovoltaic material 142, resulting in a change in theelectrical properties of the circuit 140. Based on the change in theelectrical properties of the circuit 140, the processor 116 of thecontrol unit 102 may determine the presence or concentration of arefrigerant gas in the sample 104 collected from the monitored gasvolume 106. The illustrated embodiment also includes an outlet 113 whichallows the gas to flow out of the UV tracer detection unit 114 aftermeasuring the presence or concentration of UV tracers in the sample gasflow 122

FIG. 11 is a flow diagram illustrating an embodiment of a process 146for operating the UV tracer sensor 100, in accordance with presenttechniques. It is to be understood that the steps discussed herein aremerely exemplary, and certain steps may be omitted or performed in adifferent order than the order discussed herein. In some embodiments,the process 146 may be stored in the non-volatile memory 88 and executedby the microprocessor 86 of the control panel 82, or stored in thememory 118 and executed by the processor 116 of the control unit 102, orstored in other suitable memory and executed by other suitableprocessing circuitry.

The illustrated embodiment of the process 146 begins with themicroprocessor 86 providing control signals to cycle the vaporcompression system 72 of the HVAC system into an off-cycle or idlestate, as indicated in block 148. For example, the control signal maydeactivate the motor 94 of the compressor 74, as well as fans associatedwith condenser 76 and/or evaporator 80. It is presently recognized that,in certain embodiments, it is advantageous to operate the UV tracersensor 100 when the HVAC system is idle, especially when the UV tracersensor 100 is disposed near the evaporator 80. For example, the UVtracer may be disposed within the casing 110 of the indoor HVAC unit 56,as discussed above, or below the evaporator 80. That is, it isrecognized that leaked refrigerant may accumulate in this region in theabsence of the air flow present when the HVAC system is operating. Forexample, operating may include when the HVAC system is in an on-state,when motor 94 of the compressor 74 and fans associated with condenser 76and evaporator 80 are activated. Additionally, it is presentlyrecognized that, by checking for a refrigerant leak between on-cycles ofthe HVAC system, the microprocessor 86 can subsequently preventreactivation of the HVAC system, preventing the risk of substantialdamage to the HVAC system or the building. In certain embodiments, themicroprocessor 86 of the control unit 102 of the UV tracer sensor 100may receive a suitable signals from the microprocessor 86 of the controlpanel 82 to determine when the HVAC system is in an off-cycle. Forembodiments in which the microprocessor 86 of the control panel 82executes the process 148, the microprocessor 86 may provide controlsignals to deactivate the HVAC system before proceeding to the next stepof the illustrated process 146. For example, deactivating the HVACsystem may include placing the HVAC system in an off-cycle ordeactivating the motor 94 of the compressor 74 and fans associated withcondenser 76 and evaporator 80.

Once the vapor compression system 72 of the HVAC system is in anoff-cycle, the microprocessor 86 provides suitable control signals toprepare the UV tracer sensor 100 for measurement, as indicated in block150. In certain embodiments, preparing the UV tracer sensor 100 caninvolve calibrating the one or more light detectors 126 of the UV tracerdetection unit 114. For example, this may involve recording baselinemeasurements from the UV tracer detection unit 114 before the sample 104is collected. The baseline areas are later used for comparison tomeasurements obtained after the sample 104 reaches the light detectors126. In particular, depending on the components of the UV tracerdetection unit 114, calibrating can involve measuring an initial lightintensity from the UV light source 124 by the light detector 126.

After the UV tracer sensor 100 is prepared, the microprocessor 86 of thecontrol unit 102 provides suitable control signals to the samplepreparation unit 112 to activate gas flow to collect the sample 104 fromthe monitored gas volume 106, as indicated in block 152. For example,for the embodiment of the UV tracer sensor 100 illustrated in FIG. 5,this involves the microprocessor 86 providing suitable control signalsto modify the valve 108 to an open position, and potentially activatinga suitable air moving device, to draw in the sample and generate thefirst gas flow 114. In certain embodiments where a background signal isnot determined in block 150, activating a gas flow is an optional step.In these embodiments, the microprocessor 86 provides control signals tothe UV tracer sensor 100 to sample gas, as indicated in block 154. Forexample, sample gas flow 122 is delivered to the UV tracer sensor 100 byhaving the UV tracer sensor 100 disposed in a suitable position forreceiving an air stream generated by the HVAC systems or by simplediffusion.

Continuing through the embodiment of the process 146 illustrated in FIG.11, the microprocessor 86 of the control panel 82 then receives signalsindicative of the detection of UV tracers from the light detector 126 ofthe UV tracer detection unit 114, as indicated in block 156. Asdiscussed above, the signals provided by the UV tracer detection unit114 may be derived from optical and/or electrical signals based on thepresence of UV tracers that interact with light from the UV lightdetectors that may be present in the sample gas flow 122.

Continuing through the embodiment of the process 146 illustrated in FIG.11, the microprocessor 86 of the control panel 82 then determines apresence or a concentration of refrigerant within the sample 104 basedat least in part on the signals received from the light detector 126, asindicated in block 158. For example, in certain embodiments, the controlpanel 82 may store, in the memory 88, look-up tables that relatemeasurement signals received from the light detector 126 with knownconcentrations of leaked refrigerant based on design experimentation. Inother embodiments, any significant change in a measurement signal mayprovide a binary indication of the presence of the refrigerant in thesample 104 and the monitored gas volume 106. As illustrated, when themicroprocessor 86 determines that refrigerant is not present in thesample 104, then the microprocessor 86 provides control signals to thevapor compression system 72 of the HVAC system 12 for the vaporcompression system 72 to resume normal operation, based on the demandsof the building 10, as indicated in block 159.

Subsequently, the microprocessor 86 of the control panel 82 maydetermine whether the determined presence or concentration ofrefrigerant is sufficient for corrective action to be taken, or if it islow enough to be taken as a false positive, as indicated in block 160.For example, in certain embodiments, the control unit 102 may store inthe memory 88 a threshold value associated with a refrigerantconcentration. As such, in block 160, the microprocessor 86 may comparethe current determined concentration of the refrigerant to the storedthreshold value. As illustrated, when the microprocessor 86 determinesthat the presence or concentration of the refrigerant is notsufficiently high, then the microprocessor 86 provides control signalsto the vapor compression system 72 of the HVAC system 12 for the vaporcompression system 72 to resume normal operation, based on the demandsof the building 10, as indicated in block 161.

When the microprocessor 86 determines that the concentration ofrefrigerant is sufficiently high to warrant modifying operation of theHVAC system, then the microprocessor 86 may provide suitable signals tocause the HVAC system to take corrective action and disable on-cycleoperation of the HVAC system, as indicated in block 162. For example, incertain embodiments, the microprocessor 86 provides signals to block orprevent the HVAC system from returning to an active state, as indicatedin block 164. In certain embodiments, any amount of detected refrigerantis considered sufficiently high to trigger the microprocessor 86 to takecorrective action. Additionally, in certain embodiments, the correctiveaction of block 162 may include the microprocessor 86 providing suitablesignals to generate an alarm 166 or an alert 168 on a device associatedwith the HVAC system or on a device of an occupant of the building 10,to inform people of the detected refrigerant leak. For example, thedevice may be a computer or a mobile device. Further, in certainembodiments, the corrective action of block 162 may include themicroprocessor 86 providing suitable signals to activate fans associatedwith the ductwork of the HVAC system to disperse the leaked refrigerantwithin or outside of the building 10. For example, fans associated withthe ductwork 14 and/or 68 may disperse the leaked refrigerant into alarger volume to dilute to the leaked refrigerant to a reducedconcentration. For embodiments in which an exhaust ventilation featureis present in the HVAC system and/or the building 10, fans associatedwith this exhaust feature may direct and disperse the leaked refrigerantoutside of the building 10.

Accordingly, the present disclosure is directed to an UV tracer sensorthat enables the detection and mitigation of refrigerant leaks. The UVtracer sensor generally detects UV tracers in a monitored gas volume. Inone embodiment, the UV tracer sensor is designed to measure changes inthe optical properties of light from UV light sources. In anotherembodiment, the UV tracer sensor measures changes in the electricalproperties of components of the UV light sensor. As discussed above,these changes may occur as a result of interactions between UV tracersand UV light sources of the UV tracer detection unit of the UV tracersensor. Accordingly, operation of the HVAC system can be controlledbased, at least in part, on signals received from the disclosed UVtracer sensor. For example, in response to determining that theconcentration of refrigerant is sufficiently high, a suitable processor116 may provide control signals to take corrective action. For example,corrective action may include transmitting an alert indicative of theconcentration of the refrigerant, or stopping operation of the HVACsystem. In this manner, the disclosed UV tracer detector may improveoperation of the HVAC system while enabling the detection and mitigationof refrigerant leaks substantially before the refrigerant may reach thepredefined concentration threshold.

While only certain features and embodiments of the present disclosurehave been illustrated and described, many modifications and changes mayoccur to those skilled in the art. For example, modifications mayinclude variations in sizes, dimensions, structures, shapes andproportions of the various elements, values of parameters, mountingarrangements, use of materials, and orientations, without materiallydeparting from the novel teachings and advantages of the subject matterrecited in the claims. The order or sequence of any process or methodsteps may be varied or re-sequenced according to alternativeembodiments. It is, therefore, to be understood that the appended claimsare intended to cover all such modifications and changes as fall withinthe true spirit of the disclosure. Furthermore, in an effort to providea concise description of the embodiments, all features of an actualimplementation may not have been described. For example, those unrelatedto the presently contemplated best mode of carrying out of thedisclosure, or those unrelated to enabling the claim features may nothave been described It should be appreciated that in the development ofany such actual implementation, as in any engineering or design project,numerous implementation specific decisions may be made. Such adevelopment effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure, without undue experimentation.

1. A leak detection system of a heating, ventilating, and airconditioning (HVAC) system, comprising: a sensor configured to detect anultraviolet (UV) tracer in a monitored gas volume of the HVAC system;and a controller communicatively coupled to the sensor, wherein thecontroller is configured to modify operation of the HVAC system inresponse to the sensor detecting the UV tracer in the monitored gasvolume.
 2. The system of claim 1, wherein the sensor is configured tomeasure a concentration of the UV tracer within the monitored gasvolume.
 3. The system of claim 1, wherein the controller is configuredto determine a concentration of leaked refrigerant in the monitored gasvolume based on the measured concentration of the UV tracer within themonitored gas volume.
 4. The system of claim 3, wherein the controlleris configured to modify the operation of the HVAC system when theconcentration of the leaked refrigerant in the monitored gas volume isgreater than a predetermined threshold value.
 5. The system of claim 1,comprising a sample preparation unit configured to collect a gas samplefrom the monitored gas volume and to prepare the gas sample for UVanalysis.
 6. The system of claim 5, comprising a valve communicativelycoupled to the controller, wherein the valve is configured to actuate tocollect the gas sample from the monitored gas volume in response tocontrol signals from the controller.
 7. The system of claim 5, whereinthe sample preparation unit comprises a compressor configured tocompress the gas sample to prepare the gas sample for the UV analysis.8. The system of claim 1, wherein the sensor comprises a UV tracerdetection unit configured to detect a concentration of the UV tracer ina sample collected from the monitored gas volume.
 9. The system of claim8, wherein the UV tracer detection unit comprises: a light sourceconfigured to irradiate the gas sample with emitted light; and a lightdetector configured to detect modified light from the gas sample,wherein the emitted light interacts with the sample to generate themodified light.
 10. The system of claim 9, wherein the sensor isconfigured to use a difference between an intensity of the emitted lightand an intensity of the modified light to detect the concentration ofthe UV tracer in the sample.
 11. The system of claim 9, wherein afrequency of the emitted light is different than a frequency of themodified light, and wherein the sensor is configured to correlate anintensity of the modified light with the concentration of the UV tracerin the sample.
 12. The system of claim 9, wherein the controller isconfigured to correlate the UV tracers being present in the sample. 13.The system of claim 9, wherein the UV tracer detection unit comprises areflective surface configured to direct the emitted light to the sample.14. The system of claim 9, wherein the UV tracer detection unitcomprises a reflective surface configured to direct modified light tothe light detector.
 15. The system of claim 9, wherein the UV tracerdetection unit comprises a plurality of reflective surfaces, wherein theplurality of reflective surfaces is configured to cooperate to directthe emitted light to the gas sample, to direct the modified light to thelight detector, or a combination thereof.
 16. The system of claim 13,wherein the reflective surface is a surface of a duct of the HVACsystem.
 17. The system of claim 9, wherein the light detector comprisesa camera configured to detect the modified light from the gas sample.18. The system of claim 9, wherein the light detector comprises aphotovoltaic device that is configured to detect the modified light fromthe gas sample.
 19. The system of claim 1, wherein the sensor isdisposed within a duct of the HVAC system, and wherein the monitored gasvolume comprises conditioned air within the HVAC system.
 20. The systemof claim 1, wherein the sensor is disposed within a casing of aninterior HVAC unit of the HVAC system, and wherein the monitored gasvolume is within the casing of the interior HVAC unit.
 21. The system ofclaim 20, wherein the HVAC system comprises an evaporator disposedwithin the casing of the interior HVAC unit, and wherein the UV tracersensor is disposed near the evaporator.
 22. The system of claim 1,wherein the sensor is disposed within a casing of an exterior HVAC unitof the HVAC system, and wherein the monitored gas volume is within thecasing of the exterior HVAC unit.
 23. The system of claim 1, wherein theHVAC system comprises a condenser disposed within the casing of theexterior HVAC unit, and wherein the UV tracer sensor is disposed nearthe condenser.
 24. A leak detection system of a heating, ventilating,and air conditioning (HVAC) system, comprising: a vapor compressionsystem configured to circulate a refrigerant that includes anultraviolet (UV) tracer; a sensor configured to measure a concentrationof the UV tracer in a monitored gas volume near the vapor compressionsystem of the HVAC system; a controller configured to: determine aconcentration of refrigerant in the monitored gas volume based on theconcentration of the UV tracer measured by the sensor; and modifyoperation of the HVAC system when the concentration of refrigerant inthe monitored gas volume is greater than a predetermined thresholdvalue.
 25. The system of claim 24, wherein the sensor is configured tocollect a gas sample from the monitored gas volume when the controllerdetermines that the HVAC system is idle.
 26. The system of claim 24,wherein the vapor compression system comprises an evaporator, andwherein the sensor is disposed near the evaporator.
 27. The system ofclaim 24, comprising a sample preparation unit fluidly coupled to a UVtracer detection unit of the sensor, wherein the sample preparation unitis configured to collect a gas sample from the monitored gas volume andprepare the gas sample, and wherein the UV tracer detection unit isconfigured to measure the concentration of the UV tracer in the gassample.
 28. The system of claim 27, wherein the sample preparation unitcomprises a compressor configured to compress the gas sample before theUV tracer detection unit measures the concentration of the UV tracer inthe gas sample.
 29. The system of claim 24, wherein the sensor comprisesa UV tracer detection unit comprising a light source configured toirradiate the gas sample with emitted light and a light detectorconfigured to detect modified light from the gas sample, and wherein themodified light has a reduced intensity, a different frequency, or acombination thereof, compared to the emitted light due to interactionsbetween the emitted light and the gas sample.
 30. The system of claim29, wherein the UV tracer detection unit comprises a plurality ofreflective materials configured to cooperate to direct the emitted lightto the gas sample, to direct the modified light to the light detector,or a combination thereof.
 31. The system of claim 30, wherein thereflective materials are disposed along an inner surface of a casing ofan indoor HVAC unit or outdoor HVAC unit of the HVAC system.
 32. Thesystem of claim 29, wherein the light detector comprises a camera or aphotovoltaic device configured to detect the modified light from the gassample.
 33. The system of claim 24, wherein the sensor is disposedwithin a duct of the HVAC system, and wherein the monitored gas volumecomprises conditioned air within the HVAC system.
 34. A method ofoperating a sensor to detect a refrigerant in a monitored gas volumeassociated with a heating, ventilation, and air conditioning (HVAC)system, the method comprising: collecting a sample from the monitoredgas volume; measuring an amount of ultraviolet (UV) tracer in thesample; determining an amount of refrigerant present in the monitoredgas volume based at least in part on the measured amount of UV tracer inthe sample; and modifying operation of the HVAC system in response todetermining that the amount of refrigerant present in the monitored gasvolume is greater than a predetermined threshold value, whereinmodifying comprises at least impeding the HVAC system from activating.35. The method of claim 34, comprising disabling activation of the HVACsystem before collecting the sample.
 36. The method of claim 34,comprising preparing the sensor before collecting the sample.
 37. Themethod of claim 34, wherein modifying operation comprises activating oneor more fans associated with ductwork of the HVAC system.